1. Field of the Invention
The present invention relates to a system for a large amount of expression or secretion of a protein or peptide in Humicola microorganisms, in particular, Humicola insolens. 
2. Description of the Related Art
Mold fungi is known to secrete proteins extracellularly. Thus, has been studied for developing highly productive mutant cells and processes for efficient production of proteins.
A typical example of such studies is to artificially create mutants by exposure to ultraviolet rays or by the use of a mutagen, and to select a strain which produces the target protein in a large volume.
However, these techniques may not be suitable for expressing an enzyme whose activity relies on the coordination of several different proteins, or for improving the characteristics of such an enzyme. Furthermore, when producing a protein which imparts a lethal or adverse effect on the growth of a host cell, the productivity of the target protein is generally difficult to increase by a mutation.
On the other hand, the recent progress in the study of genetic recombination for producing a target protein have enabled a large amount of production for heterogenous proteins, as well as proteins endogenous to the host cells but expressed only in small amounts. Successful production ranging from about 1.0 to 3.3 g per one liter of culture has been reported in some mold fungi, such as Aspergillus nidulans (G. L. Gray, et al., Gene, 48,41, 1986), Aspergillus oryzae (T. Christensen, et al., Bio/Technology, 6, 1419, 1988), Trichoderma reesei (Taina Karhunen, et al., Mol. Gen. Genet. 241, 515-522, 1993), and Trichoderma viride (C. Cheng, et al., Agric. Biol. Chem., 55, 1817, 1991).
Humicola insolens is another example of a halophilic mold fungus having remarkable capability of protein secretion. This species is also known to produce various types of cellulase of industrial utility (WO91/17243 (Japanese Patent Laid-Open No. 5-509223)).
However, the useful content of the protein secretion from Humicola insolens accounts only for a few percent. If a process which enables fungus to express and secrete these small proportions of useful components in a large quantity is established, the benefit of the final products can be dramatically improved. Furthermore, a process that would enable a large quantity of expression of heterogenous genes in Humicola insolens may allow various enzymes and useful proteins to be produced in a single-step procedure, helping lower the cost of production. In addition, since Humicola insolens is a halophilic mold fungus with an optimum incubation temperature of about 37xc2x0 C., it is hardly contaminated by other germs during incubation, making it further advantageous as a host for producing useful proteins.
Furthermore, systems for transforming Humicola insolens have been established, as has been disclosed by some of the inventors in Japanese Patent Laid-Open No. 8-56663, allowing the fungus to be used for genetic recombination.
Still, it has been awaited to develop an effective expression vector system which allows Humicola insolens to express and secrete a target protein at a high yield.
The inventors have now established a process for producing a target protein in a large quantity in Humicola, in particular, Humicola insolens. 
Thus, the object of the present invention is to a provide expressing systems enabling production of a protein in a large amount in Humicola, in particular, Humicola insolens, and particularly host-vector systems and a process for producing a protein using the host-vector systems.
Moreover, according to the preferred embodiment of the present invention, there is provided a highly efficient system for producing a protein, in which the productivity of the target protein is as high as about 4.5 g per one liter of culture, or 10 to 16 times that in the original strain.